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  • The Geological Survey of Western Australia, in collaboration with the Australian National University, Macquarie University, the Department of Fire and Emergency Services and Geoscience Australia has just installed the first seismometers of an array across the South West Seismic Zone of Western Australia. This region is one of the most seismically active areas of Australia having experienced over 2000 small (between ML 2 to 3) earthquakes since the year 2000. Many smaller events are also noted by the local people who often hear them coming. Yes – hear them coming – this area is known for its “noisy” earthquakes. Most of these earthquakes occur in swarms rather than main shock-aftershock sequences (Dent, 2015). This means that the region experiences a lot of small earthquakes, all much the same size and which occur in a similar area. These swarms can be active for years. The hazard associated with these seismic events is relatively small. However, in the past six decades this region has also hosted five of the nine surface rupturing earthquakes in Australia, most notably; Meckering (M 6.5) in 1968 from which there are photos of the bends in the railway lines (Fig 1a) and faulting of 2-3 m in height across the fields (Fig 1b) (Gordon and Lewis 1980; Johnston and White 2018, Clark and Edwards 2018); Calingiri (M5.9) in 1970 and Lake Muir (M5.6), which was felt by a lot of people across Western Australia just two years ago (Clark et al. 2020). Despite the high rates of seismicity, seismic monitoring in the region remains relatively sparse. To overcome this lack of instrumentation, the consortium of institutions mentioned above, came together for an ARC Linkage project to put in place a temporary network- the South West Australia Network (SWAN) - to improve the monitoring and detection capabilities in this area. This project will see a total of twenty-five broadband seismometers deployed across the Southwest of Western Australia for a period of approximately 2 years (Fig 2a and b). This temporary array will enable the detection and location of smaller-magnitude earthquakes which can be used to improve the crustal velocity models which in turn enables more accurate earthquake locations and helps the understanding of the crustal structure of this part of Australia. Better velocity models also enable better magnitude calculation methods, which improve the knowledge about recurrence of earthquakes of a certain magnitude. From a seismic hazard point of view, this data has the potential to assist in the development of improved methods for modelling how shaking intensity varies as it propagates through the earth’s crust from the earthquake source. Overall, this information will feed into an improved understanding of the earthquake hazard in the Southwest region of Western Australia. For local communities, it will provide an improved situational awareness following significant earthquakes. More broadly, the improved understanding of the seismicity of the Southwest of Western Australia will enhance emergency response capabilities, and inform building codes and mitigation initiatives, which are the best methods we have to minimise the earthquake risks to communities. Data will be released through AusPASS, the Australian Passive Seismic Server two years after the last data has been collected.

  • You may not realise it but, on average, Australia is rattled every few days by an earthquake of magnitude 3 or above. We don’t feel every small tremor that happens, but the larger earthquakes are powerful enough to cause serious damage to buildings and infrastructure, putting our community’s safety at risk.

  • The Earthquake Scenario Selection is an interactive tool for querying, visualising and downloading earthquake scenarios. There are over 160 sites nationally with pre-generated scenarios available. These represent plausible future scenarios that can be used for earthquake risk management and planning (see https://www.ga.gov.au/about/projects/safety/nsha for more details).

  • The local magnitude ML 5.4 (MW 5.1) Moe earthquake on 19 June 2012 that occurred within the Australian stable continental region was the largest seismic event for the state of Victoria for more than 30 years. Seismic networks in the southeast Australian region yielded many high-quality recordings of the moderate-magnitude earthquake mainshock and its largest aftershock (ML 4.4; MW 4.3) at a hypocentral range of 10 to 480 km. The source and attenuation characteristics of the earthquake sequence are analyzed. Almost 15,000 felt reports were received following the main shock, which tripped a number of coal-fired power generators in the region, amounting to the loss of approximately 1955 megawatts of generation capacity. The attenuation of macroseismic intensities are shown to mimic the attenuation shape of Eastern North America (ENA) models, but require an inter-event bias to reduce predicted intensities. Further instrumental ground-motion recordings are compared to ground-motion models (GMMs) considered applicable for the southeastern Australian (SEA) region. Some GMMs developed for ENA and for SEA provide reasonable estimates of the recorded ground motions of spectral acceleration within epicentral distances of approximately 100 km. The mean weighted of the Next Generation Attenuation-East GMM suite, recently developed for stable ENA, performs relatively poorly for the 2012 Moe earthquake sequence, particularly for short-period accelerations.

  • At its nearest, northern Australia is just over 400 km from an active convergent plate margin. This complex and unique tectonic region combines active subduction and the collision of the Sunda-Banda Arc with the Precambrian North Australian Craton (NAC) near the Timor Trough and continues through to the New Guinea Highlands. Ground-motions generated from earthquakes on these structures have particular significance for northern Australian communities and infrastructure projects, with several large earthquakes in the Banda Arc region having caused ground-shaking-related damage in the northern Australian city of Darwin over the historical period. There are very few, if any, present-day tectonic analogs where cold cratonic crust abuts a convergent tectonic margin with subduction and continent-continent collision. Ground motions recorded from earthquakes in typical subduction environments are highly attenuated as they travel through young sediments associated with forearc accretionary prisms and volcanic back-arc regions. In contrast, seismic energy from earthquakes in the northern Australian plate margin region are efficiently channelled through the low-attenuation NAC, which acts as a waveguide for high-frequency earthquake shaking. As such, it is difficult to select models appropriate to the region for seismic hazard assessments. The development of a far-field ground-motion model to support future seismic hazard assessments for northern Australia is discussed. In general, the new model predicts larger ground motions in Australia from plate margin sources than models used for the 2018 National Seismic Hazard Assessment of Australia, none of which were considered fully appropriate for the tectonic environment. Short-period ground motions are strongly dependent on hypocentral depth and are significantly higher than predictions from commonly-used intraslab ground-motion models at comparable distances. The depth dependence in ground motion diminishes with increasing spectra periods. <b>Cite this article as</b> Allen, T. I. (2021). A Far-Field Ground-Motion Model for the North Australian Craton from Plate-Margin Earthquakes, <i>Bull. Seismol. Soc. Am. </i><b> 112</b>, 1041–1059, doi: 10.1785/0120210191

  • Seismic hazard models, commonly produced through probabilistic seismic hazard analysis, are used to establish earthquake loading requirements for the built environment. However, there is considerable uncertainty in developing seismic hazard models, which require assumptions on seismicity rates and ground-motion models (GMMs) based on the best evidence available to hazard analysts. This paper explores several area-based tests of long-term seismic hazard forecasts for the Australian continent. ShakeMaps are calculated for all earthquakes of MW 4.25 and greater within approximately 200 km of the Australian coastline using the observed seismicity in the past 50 years (1970-2019). A “composite ShakeMap” is generated that extracts the maximum peak ground acceleration “observed” in this 50-year period for any site within the continent. The fractional exceedance area of this composite map is compared with four generations of Australian seismic hazard maps for a 10% probability of exceedance in 50 years (~1/500 annual exceedance probability) developed since 1990. In general, all these seismic hazard models appear to be conservative relative to the observed ground motions that are estimated to have occurred in the last 50 years. To explore aspects of possible prejudice in this study, the variability in ground-motion exceedance was explored using the Next Generation Attenuation-East GMMs developed for the central and eastern United States. The sensitivity of these results is also tested with the interjection of a rare scenario earthquake with an expected regional recurrence of approximately 5,000 - 10,000 years. While these analyses do not provide a robust assessment of the performance of the candidate seismic hazard for any given location, they do provide—to the first order—a guide to the performance of the respective maps at a continental scale. This paper was presented at the Australian Earthquake Engineering Society 2021 Virtual Conference, Nov 25 – 26.

  • A database of recordings from moderate-to-large magnitude earthquakes is compiled for earthquakes in western and central Australia. Data are mainly recorded by Australian National Seismograph Network (ANSN), complemented with data from temporary deployments, and covering the period of 1990 to 2019. The dataset currently contains 1497 earthquake recordings from 164 earthquakes with magnitudes from MW 2.5 to 6.1, and hypocentral distances up to 1500 km. The time-series data are consistently processed to correct for the instrument response and to reduce the effect of background noise. A range of ground-motion parameters in the time and frequency domains are calculated and stored in the database. Numerous near-source recordings exceed peak accelerations of 0.10 g and range up to 0.66 g, while the maximum peak velocity of the dataset exceeds 27 cm/s. In addition to its utility for engineering design, the dataset compiled herein will improve characterisation of ground-motion attenuation in the region and will provide an excellent supplement to ground-motion datasets collected in analogue seismotectonic regions worldwide. This paper was presented at the Australian Earthquake Engineering Society 2021 Virtual Conference, Nov 25 – 26.

  • Public concerns have been raised about the potential for induced seismicity as state and territory governments lift moratoriums on hydraulic stimulation activities for the exploration and extraction of unconventional hydrocarbons. The Scientific Inquiry into Hydraulic Fracturing in the Northern Territory articulated the need for a traffic-light system “to minimise the risk of occurrence of seismic events during hydraulic fracturing operations” within the Beetaloo Sub-basin. A temporary seismic network (Phase 1) was deployed in late 2019 to monitor baseline seismic activity in the basin. Based on the data analysed herein (November 2019 – April 2021), no seismic events were identified within the area of interest suggesting that the Beetaloo Sub-basin is largely aseismic. Observations to date indicate that there is potential to identify events smaller than ML=1.5 within the basin. The recent installation of ten semi-permanent stations for continuous real-time monitoring will contribute to ongoing baseline monitoring efforts and support the implementation of an induced seismicity traffic-light system. The outcome of this study will be used to build knowledge about potential human-induced seismic activity in the region that may be associated with unconventional hydrocarbon recovery. This paper was presented at the Australian Earthquake Engineering Society 2021 Virtual Conference, Nov 25 – 26.

  • Here we undertake a statistical analysis of local magnitudes (ML) calculated using the two real-time earthquake monitoring software platforms use by Geoscience Australia (GA) since 2005, Antelope and Seiscomp. We examine a database of just over 10 years duration, during a period in which both systems were in operation and over 4000 earthquakes were located and magnitudes estimated. We examine the consistency of both single-station and network ML estimates of both systems, with a view toward determining guidelines for combining them into a single catalogue, as well as for determining best practice in the for the estimation of local magnitudes for regions of sparse seismic networks. Once this guidance has been developed, it is the intention of GA to re-process magnitudes for all earthquakes using a consistent approach where digital data are available and can be integrated within the currently-used SeisComP system. This paper was presented at the Australian Earthquake Engineering Society 2021 Virtual Conference, Nov 25 – 26.

  • The Mwp 6.1 Petermann Ranges earthquake that occurred on 20 May, 2016 in the Central Ranges, NT, is the largest onshore earthquake to be recorded in Australia since the 1988 Tennant Creek sequence. While geodetic and geophysical analyses have characterized the extent of surface rupture and faulting mechanism respectively, a comprehensive aftershock characterization has yet to be performed. Data has been acquired from a 12-station temporary seismic network deployed jointly by the ANU and Geoscience Australia (GA), collected from five days following the mainshock to early October. Taking advantage of enhanced automatic detection techniques using the SeisComP3 real-time earthquake monitoring software within the National Earthquake Alerts Centre (NEAC) at GA, we have developed a comprehensive earthquake catalogue for this mainshock-aftershock sequence. Utilising the NonLinLoc location algorithm combined with a Tennant Creek-derived velocity model, we have preliminarily located over 5,800 aftershocks. With additional spatio-temporal analyses and event relocation, our objective will be to use these aftershocks to help delineate the geometry of the headwall rupture along the Woodroffe Thrust. These high-resolution aftershock detection techniques are intended to be implemented in real-time within the NEAC following future significant Australian intraplate earthquakes. This paper was presented at the Australian Earthquake Engineering Society 2021 Virtual Conference, Nov 25 – 26.